The invention relates generally to metal spinning processes and apparatus and products made thereby, and more particularly to metal spinning processes and apparatus forming necked-down portions on thin walled, deep drawn, seamless steel cans.
Two commercially available processes and apparatus have been used to form necked down portions on aluminum cans, such as twelve ounce (12 oz.) soda cans, to provide suitable flange area for attaching a cover or lid and the well known six ring plastic carrying device.
The first process and apparatus, developed by Metal Box Company of England, uses two metal forming roller tools, a rotating chuck and rotating baseplate to form the neck-downed portion of the cans. A prenecked can is placed on the baseplate and clamped into position by the chuck. Compressed air is pumped into the can. The assembly is rotated at high speed and moves axially as the roller tools move inwardly forming the neck. As the baseplate moves away from the chuck, the can slips off the chuck thereby producing the familiar flange on the neck found on such cans. Prenecked cans are required by this process and are often die necked. However, prenecked cans formed by metal spinning are often used as well.
The other process is called a "spin flow" process. The neck of the can is formed in a single operation but a second operation is needed to flatten the flange to the desired angle. This process uses one metal forming roller tool, and a rotating baseplate with a slide roll (chuck) and an eccentric roll inside the can being formed.
While these two commercially available processes and apparatus work satisfactorily to produce cans from aluminum which is an easily formable material, they have not proved effective in producing necked-down portions on thin walled, deep drawn, seamless steel cans for use as, for example, aerosol cans for hair spray and the like. In addition, the material cost for an aluminum can is dramatically more expensive than that for a steel can so substantial savings can be achieved by using steel cans rather than aluminum cans.
Heretofore, metal spinning of such thin walled, deep drawn, seamless steel cans has been done using a metal insert within the can to be formed to prevent wrinkling of the can as it is worked by the metal forming roller tool. The metal insert has the desired final shape of the can and is made in a plurality of wedge shaped segments which can be manipulated and removed from the finished can. While this type of metal insert has been satisfactorily used to form necked-down portion on steel cans, it is time consuming and difficult to manipulate the wedge shaped segments from the finished can.
The present invention is designed to overcome the above noted limitations that are attendant upon the use of the "prior art" devices, and toward this end, it contemplates the provision of a novel metal method spinning method and apparatus for producing a necked-down portion on metal containers.
It is an object of the present invention to provide a novel method and apparatus using a pressure regulated bladder inserted within the container being formed during the forming of the necked-down portion thereof.
It is also an object to provide such a method and apparatus which can form the desired necked-down portion on the container in a expedited manner.
Still another object is to provide such a method and apparatus in which the containers are necked-down in a single operation without the need for prenecked cans.
An additional object is to provide such a method and apparatus which operates on thin walled, deep drawn seamless steel cans to form a necked-down portions thereon.
A further object is to provide a novel container made by the novel method and apparatus of the present invention. The novel container can be readily and economically fabricated and will enjoy a long life in service.